This invention relates to a novel suspension system for track driven vehicles, such as snowmobiles, in which a rigid chassis frame is slidably supported on a ground engaging endless track, and a snowmobile body is yieldably resiliently supported from the rigid frame by front and rear suspension or support frames arranged in a particular manner.
In prior snowmobile suspension systems, various constructions were employed to yieldably resiliently support the snowmobile body and to improve its ride over varying types of terrain. Torsion springs on front and/or rear suspension frames were used; however, the geometry of the frames and springs relative to the rigid frame and body provided a flat spring response curve over the generally vertical travel of the body relative to the frame. In some instances, linkage means were incorporated with the suspension system to modify the spring response so that the snowmobile could accommodate varying loads and various sized irregularities and bumps in the ground surface (see U.S. Pat. No. 4,093,033). Shock absorbers and other dampening means were used to obtain a desired ride under widely varying terrain conditions. Such prior snowmobile suspension systems have been the subject of continual examination and analysis in order to minimize their disadvantages and to achieve improved ride characteristics.
Generally speaking, a snowmobile suspension system should have maximum suspension travel within the space limitations of snowmobile construction, a soft response or reaction to irregularities of small magnitude in the terrain, that is, a low spring rate or resistance of the suspension system reacting to such small irregularities; and a high response, spring rate or resistance to large irregularities in the terrain. Depending upon the distribution of loads carried by the snowmobile body and the desired ride characteristics, front and rear suspension frames or assemblies may be designed with different spring rates which may also vary in response along the length of travel of the suspension system.